Data from: Estimating effects of species interactions on populations of endangered species

Global change causes community composition to change considerably through time, with ever-new combinations of interacting species. To study the consequences of newly established species interactions, one available source of data could be observational surveys from biodiversity monitoring. However, approaches using observational data would need to account for niche differences between species and for imperfect detection of individuals. To estimate population sizes of interacting species, we extended N-mixture models that were developed to estimate true population sizes in single species. Simulations revealed that our model is able to disentangle direct effects of dominant on subordinate species from indirect effects of dominant species on detection probability of subordinate species. For illustration, we applied our model to data from a Swiss amphibian monitoring program and showed that sizes of expanding water frog populations were negatively related to population sizes of endangered yellow-bellied toads and common midwife toads and partly of natterjack toads. Unlike other studies that analyzed presence and absence of species, our model suggests that the spread of water frogs in Central Europe is one of the reasons for the decline of endangered toad species. Thus, studying population impacts of dominant species on population sizes of endangered species using data from biodiversity monitoring programs should help to inform conservation policy and to decide whether competing species should be subject to population management.

全球变化可导致生物群落组成随时间发生显著改变，形成持续更新的物种相互作用组合。为探究新形成的物种相互作用所产生的后果，现有可用的数据来源之一为生物多样性监测的观测调查数据。然而，基于观测数据的研究方法需兼顾物种间的生态位差异，以及个体检测不完全的局限。为估算相互作用物种的种群规模，我们对仅用于单物种真实种群规模估算的N-mixture模型（N-mixture models）进行了拓展。模拟实验结果表明，本模型能够有效区分优势物种对从属物种的直接影响，与优势物种对从属物种检测概率的间接影响。为演示模型的应用效果，我们将其应用于瑞士两栖动物监测项目的数据，结果显示：扩张中的水蛙种群规模，与濒危黄腹蟾蜍（yellow-bellied toads）、普通助产蟾（common midwife toads）以及部分犁足蟾（natterjack toads）的种群规模呈负相关关系。与其他仅分析物种存在与否的研究不同，本模型证实：中欧地区水蛙的扩散是濒危蟾蜍种群衰退的重要诱因之一。综上，借助生物多样性监测项目的数据，探究优势物种对濒危物种种群规模的影响，可为保护政策制定提供科学依据，并辅助决策是否需要对竞争物种实施种群管理。